Disengagable burr mill

ABSTRACT

A downhole tool for use in the removal of burrs or other unwanted material from an inner surface of a pipeline, well casing or other tubular. The tool has a plurality of milling elements, which may be biased against the surface or retracted from the surface to disengage the tool from the tubular. A drop ball mechanism with a fluid by-pass is described for disengaging the milling elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus and method for use in oil andgas exploration and production, in particular, but not exclusively, to aburr mill for selectively performing milling and/or burr removal withina well.

When an oil or gas well is drilled it is common to insert a liner orcasing into the well in order to support the walls as the depth of thewell is increased. In order to access oil or gas containing formationoutside the casing, the casing is commonly perforated by means ofexplosives. As the casing is made of a hardwearing material such assteel, when perforation takes place the steel casing is deliberatelydamaged to provide access from the wellbore through to the formation andas a result, sections of the casing will be left with exposed metalshards or burrs directed into the wellbore.

Consequently, the insertion of any other tools into the wellbore aresusceptible to damage due to collisions with or scraping against theburrs formed during perforation. In particular, delicate screens usedfor the filtering of fluids downhole can easily be ruptured on contactwith the burrs. It would therefore be advantageous to find a method ofremoving these burrs to avoid damaging tools downhole.

It is already known to attach a mill to a drill string and by rotationof the drill string through the wellbore, burrs may be removed. Thesetools have the disadvantage that once they have successfully milled offthe burrs they become redundant within the well and if left in placethey can both cause unwanted wear on the casing and be exerted tounwanted wear on the milling surfaces of the tool as they are subjectedto continuous buffering on the inside diameter of the casing.

It is an object of at least one embodiment of the present invention toprovide a downhole tool for the removal of burrs or other unwanteddebris from inside a wellbore which obviates or mitigates disadvantagesin the prior art.

It is an object of at least one embodiment of the present invention toprovide a downhole tool in the form of a burr mill which is disengagableso that the milling elements can be removed from the surfaces on whichthe burrs occur.

BRIEF SUMMARY OF THE INVENTION

According to the first aspect of the present invention, there isprovided a downhole tool for the removal of burrs and other unwantedmaterial from an inside surface of a pipeline, well casing or othertubular, the tool including a tool body mountable on a work string, thebody supporting a plurality of milling elements which mill the surfaceand retraction means for disengaging the milling elements from thesurface when milling is no longer required.

Thus, the tool is capable of providing a milling action to remove burrswhen the tool body is rotated on a drill string as it enters the welland at any location where the string requires to be circulated but nomilling is required, the milling elements can be disengaged andretracted back into the tool to stop their contact with the insidesurface of the casing or liner.

Preferably the tool includes biasing means to bias the one or moremilling elements in an outward radial direction. Preferably the millingelements are biased into engagement with the inside surface.Advantageously the biasing means comprise springs held undercompression. Preferably also the tool includes an outer sleeve, theouter sleeve including one or more apertures through which the millingelements protrude. More preferably the apertures include overhangingportions which engage a part of the milling element and limit the radialmovement of the milling element. By limiting the radial movement of themilling elements the springs are held in compression.

Preferably the retraction means comprises release means to remove thecompression on the springs. Advantageously the release means operates byre-positioning the springs relative to the tool body. The release meansmay comprise an inner sleeve mounted in a central bore of the tool bodyinto which are located ends of the springs. The springs arere-positioned by virtue of movement of the inner sleeve from a firstposition in which the milling elements are engaged to the inside surfaceand a second position where the milling elements are disengaged.

Preferably the inner sleeve is held in the first position by at leastone shear pin. More preferably the inner sleeve includes a ball seatinto which a drop ball can locate. Once located a pressure build upbehind the ball will force the ball against the drop inner sleeve untilthe shear pin shears and the inner sleeve falls into the secondposition.

Preferably the retraction means further includes one or more magnets.Preferably the magnets hold the milling elements against the tool bodywhen disengaged.

Preferably also the tool includes a by-pass means which maintains fluidflow through the central bore by allowing fluid to by-pass the drop ballwhen the tool is disengaged. Advantageously the by-pass means comprisesone or more radial ports in the inner sleeve and one or more recesses inthe tool body. When the inner sleeve is in the second position, the oneor more recesses are located adjacent the drop ball and one or more flowpaths are created as the one or more ports align with the one or morerecesses thereby directing fluid around the drop ball.

According to a second aspect of the present invention, there is provideda method of removing burrs or other unwanted debris from an insidesurface of a pipeline, well casing or other tubular, the methodcomprising the steps:

-   -   a) inserting into the tubular one or more milling elements;    -   b) biasing the one or more milling elements against the surface        to provide a milling action when the elements are moved in        relation to the surface;    -   c) disengaging the one or more milling elements from the surface        to prevent further milling.

Preferably the method further includes the step of actively retainingthe milling elements in a retracted position away from the surface ofthe tubular.

Preferably step (c) includes the step of dropping a ball into the toolto cause parts thereof to move in relation to each other and therebyre-position springs within the tool.

More preferably the method includes the step of magnetically retainingthe one or more milling elements against the tool body when disengaged.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

An embodiment of the present invention will now be described by way ofexample only with reference to the accompanying Figures in which:

FIGS. 1 (a) and 1 (b) are a schematic cross-sectional view of a downholetool in both an engaged (LHS) and disengaged (RHS) position inaccordance with an embodiment of the present invention;

FIG. 2 is a [top] view of a milling element of the apparatus of FIG. 1;and

FIG. 3 is a sectional view through the line X—X of FIG. 1 (b).

DETAILED DESCRIPTION OF THE INVENTION

Reference is initially made to FIG. 1 of the drawings which depicts adownhole tool generally indicated by reference numeral 10 according toan embodiment of the present invention. Tool 10 includes a tool body 12through which is axially located a central bore 14 for the passage offluid through the tool 10. At an upper end of tool body 12 is located abox section 16 and at a lower end of tool body 12 there is located athreaded pin 18. Box section 16 and threaded pin 18 allow the tool 10 tobe connected in a drill string (not shown).

Within the central bore 14 there is an inner sleeve 20. Inner sleeve 20includes four ports 22 which when the sleeve is moved can locate acrossa recess 24 in the tool body 12 and provide an alternative flow path.This is illustrated in FIG. 1 at the upper end of the tool where theinner sleeve 20 has been moved by the action of a drop ball 26 beingplaced in the central bore 14. Inner sleeve 20 is kept initially inplace by the use of shear screws 28. When ball 26 is dropped through thecentral bore 14, it lands on the ball seat at the upper end of innersleeve 20. A fluid pressure build up behind ball 26 forces the ball 26downwards with the result that the screws 28 shear under the force.Sleeve 20 then falls until it is prevented from exiting the lower end ofthe tool 10 by virtue of the lip 30.

Milling elements 32 are arranged around the tool body 12. In theembodiment shown there are three milling elements arranged equidistantlyaround the tool body as shown more clearly with the aid of FIG. 3.

Referring to FIG. 2, it is seen that each milling element has a millingsurface which is arranged with projections to aid the milling action forthe removal of burrs and other unwanted debris from the inside walls ofthe pipeline, liner or casing in use. Consequently, each milling surface34 has a radial profile to provide a match to the pipeline wall (notshown). The milling elements 32 are not fixed to the tool body 12. Themilling elements 32 are free-floating and are held in the extendedposition against the pipeline walls by virtue of springs 36, 38 and 40located between the milling elements 32 and the inner sleeve 20. To aidthe insertion of these springs 36, 38 and 40 when the tool is assembled,magnets 42 are located in recesses on a back surface 44 of the millingelement wherein each spring 36, 38 and 40 locates in the recess and isheld in place by the magnet 42. The opposing end of each spring 36, 38and 40 is held in a narrow recess 46 on the inner sleeve 20. Alsolocated on the back surface 44 of the milling element 32 are additionalretraction magnets 48 and 50. Magnets 48 and 50 are located adjacentelongate ports 52 and 54 into which are located socket head cap screws56 and 58 whose purpose will be described hereinafter.

Milling element 32 is limited in radial movement by stand off sleeves 60and 62. Each stand off sleeve 60 and 62 has opposite handed threads thusin this embodiment stand off sleeve 60 has a left hand thread whilestand off sleeve 62 has a right hand thread. Each sleeve 60 and 62includes a lip 64, 66 which engages the corresponding lip 68, 70 on themilling element 32 to prevent the radial movement. Thus, milling element32 is biased radially outwards by the use of the springs 36, 38 and 40.As better shown in FIG. 3, it will be appreciated that the springs 36and magnets 42 may be paired up. Although those skilled in the art willappreciate that any number of milling elements may be used and the sizeand arrangement of the springs may be adjusted, as long as the overalleffect is to bias the milling elements and in particular, the millingsurfaces 34 outwardly.

In use the milling elements 32 are arranged on the tool body 12 in theconfiguration shown to the left hand side of FIG. 1. The tool 10 isattached to the drill string and the drill string rotated into thecasing or liner. On entering the casing or liner the milling elementsare in the expanded position by virtue of the springs 36, 38 and 40radially biasing the milling surface 34 against the inner surface of thecasing. The milling element 32 may move in relation to the diameter ofthe casing so that casing inner diameters of various sizes can be usedwith the tool. As the tool is rotated, burrs present on the inside wallof the casing will be dressed off and removed as will any other debrison the surface of the casing walls. When it is necessary to stop ade-burring or milling process but the drill string still requires torotate to operate other tools which may be mounted thereon, a drop ball26 is released into the central bore 14 of the tool. The drop ball 26will typically be released at the surface and travel through the centralbore of the drill string to enter the tool 10 at its location in thewellbore. Drop ball 26 will close the central bore 14 as it impacts onthe inner sleeve 20. Fluid pressure will build up behind the ball 26 andthe resulting force will cause the shear screws 28 to shear therebyallowing the inner sleeve 20 to fall towards the lower end of the tool.In falling the port 22 will locate over recess 24 in the tool body 12 sothat flow is maintained through the central bore 14 of the tool 10. Atthe location of the milling elements 32, movement of the inner sleeve 20will cause the springs 36, 38 and 40 to be re-positioned longitudinallywith respect to the tool body 12. Narrow recesses 36 will ensure thatthe end of the springs 36, 38 and 40 and located in the narrow recess 46will be forced downwards which will release the opposing end of eachspring 36, 38 and 40 from the magnet 42. Once the springs 36, 38 and 40have been re-positioned, the milling element 32 will be pulled radiallyinwards by the action of the magnets 42 against the re-positionedsprings 36, 38 and 40 with the result that the milling element 32 willbe pulled to a retracted position away from the walls of the casing.Milling element 32 will be held in the retracted position by virtue ofthe retraction magnets 48 and 50 remaining attached and attracting thesocket head cap screws 56 and 58. Thus, in the disengaged position themilling elements 32 are held against the tool body 12 and the millingoperation is stopped. In order to prevent passage of fluid into theregion where the springs 36, 38 and 40 and magnets 42, 48 and 50 arelocated, the inner sleeve 20 includes a series of ‘O’ rings 72 and 74.

The principle advantage of the present invention is that it provides amilling tool where the milling elements can be disengaged to reduce wearon the elements and on the casing walls in use.

It is a further advantage of the present invention that the millingelements are held against the tool body when the tool is disengaged.

Various modifications may be made to the invention describedhereinbefore without departing from the scope thereof. For instance, thenumber and arrangement of milling elements may be varied as long as theyare mounted around the tool body and have a milling rib or profile tointeract with a surface of the inner wall of the casing. Additionally,there may be more than one set of milling ribs located longitudinallywhich can be operated by a single ball drop. It will also be appreciatedby those skilled in the art that a number of these tools may be mountedin relation to each other on a drill string each being operatedseparately by means of different sized drop balls. Thus, the lowestpositioned tool would have a small inner sleeve so that the drop ballwould be small enough to fall through the central bore and inner sleeveof the milling tools placed above it.

1. A downhole tool for the removal of burrs and other unwanted materialfrom an inside surface of a pipeline, well casing or other tubular, thetool including a tool body mountable on a work string, the bodysupporting a plurality of milling elements which mill the surface,biasing means to bias the plurality of milling elements in an outwardradial direction by springs held under compression and retraction meansfor disengaging the milling elements from the surface by repositioningof the springs when milling is no longer required.
 2. A downhole tool asclaimed in claim 1 wherein the tool further includes an outer sleeve,the outer sleeve including one or more apertures through which themilling elements protrude.
 3. A downhole tool as claimed in claim 2wherein the apertures include overhanging portions which engage a partof the milling element and limit the radial movement of the millingelement.
 4. A downhole tool as claimed in claim 1 wherein the retractionmeans comprises release means to remove the compression on the springs.5. A downhole tool as claimed in claim 4 wherein the release meanscomprises an inner sleeve mounted in a central bore of the tool bodyinto which are located ends of the springs such that the springs arere-positioned by virtue of movement of the inner sleeve from a firstposition in which the milling elements are engaged to the inside surfaceand a second position where the milling elements are disengaged.
 6. Adownhole tool as claimed in claim 5 wherein the inner sleeve is held inthe first position by at least one shear pin.
 7. A downhole tool asclaimed in claim 6 wherein the inner sleeve includes a ball seat intowhich a drop ball can locate such that a pressure build up behind theball will force the ball against the inner sleeve until the shear pinshears and the inner sleeve falls into the second position.
 8. Adownhole tool as claimed in claim 4 wherein the retraction means furtherincludes one or more magnets to hold the milling elements against thetool body when disengaged.
 9. A downhole tool as claimed in claim 7wherein the tool includes a by-pass means which maintains fluid flowthrough the central bore by allowing fluid to by-pass the drop ball whenthe tool is disengaged.
 10. A downhole tool as claimed in claim 9wherein the by-pass means comprises one or more radial ports in theinner sleeve and one or more recesses in the tool body such that whenthe inner sleeve is in the second position, the one or more recesses arelocated adjacent the drop ball and one or more flow paths are created asthe one or more ports align with the one or more recesses therebydirecting fluid around the drop ball.
 11. A method of removing burrs orother unwanted debris from an inside surface of a pipeline, well casingor other tubular, the method comprising the steps: a) inserting into thetubular one or more milling elements; b) biasing the one or more millingelements against the surface by use of springs to provide a millingaction when the elements are moved in relation to the surface; c)disengaging the one or more milling elements from the surface byrepositioning the springs to prevent further milling.
 12. A method asclaimed in claim 11 wherein the method further includes the step ofactively retaining the milling elements in a retracted position awayfrom the surface of the tubular.
 13. A method as claimed in claim 11wherein step (c) includes the step of dropping a ball into the tool tocause parts thereof to move in relation to each other and therebyre-position the springs.
 14. A method as claimed in claim 11 wherein themethod includes the step of magnetically retaining the one or moremilling elements against the tool body when disengaged.